1. Field of the Invention
The invention relates to an electronic circuit, and more particularly to a differential charge pump circuit.
2. Description of Related Art
Phase lock loop (PLL) circuit has a long history of development process and still plays a key role in technique discussions due to its wide application and high development potential. In brief, a basic function of the PLL circuit is to use an oscillation source with an extremely low variation to serve as a basic reference, and drive a device with a variable frequency under a feedback function of a closed loop control system, so that the frequency of the device is quickly and stably maintained at a same phase with the oscillation source, i.e. the frequency is phase locked.
For the PLL circuit, the charge pump (CP) is an important section for providing a real-time voltage to the voltage control oscillator (VCO). For the CP circuit, the required voltage is controlled by a signal modulated by the phase frequency detector (PFD). This voltage determines the oscillation frequency of the VCO. Once the oscillation frequency becomes too low, the CP controlled by the PFD would increase the voltage so as to increase the oscillation frequency of the VCO. On the contrary, once the oscillation frequency becomes too high, the voltage would be decreased to further decrease the oscillation frequency of the VCO.
On the other hand, for PLL circuit design, it can be categorized into single-ended architecture and differential architecture. The differential architecture may broaden the modulation range of the VCO, but the design for the CP circuit should also change to the differential architecture correspondingly. However, the conventional differential CP circuit requires a large amount of current to maintain a desire voltage. The current consumption for the conventional differential CP circuit is too much. Furthermore, a mismatch issue may occur due to the large amount of current.